The difference is between enzymes which accept CO2 from the air. C3 plants use enzym ribulosodiphosphatcarboxylase while C4 and CAM plants use phosphoenolpyruvatcarboxylase to accept CO2 from the air. Also the primary product of photosynthesis of C3 plants is phosphoglycerat while in C4 plants it is oxalacetate The differences are also between structure of the photosynthetic apparat. I hope this helps, also hope you know what enzymes are.

The difference occurs in photosynthesis. From the point of view of the first subsance created, there are 3 types of plants: C3, C4 and CAM
As protozoan pointed out C3 plants use RuDP carboxylase to fix CO2 and the first organic molecule created is phosphoglycerat(this thing has 3 C atoms=> the name C3)
C4 plants use PEP carboxylase to fix CO2 and the first organic molecule is oxalacetic acid(4 C atoms, from which comes the name). At the C4 plants photosynthesis is 6 times faster than C3 plants
There is a third kind, the CAM plants. Would you like me to explaint those to u to?

"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

From what i know, NO. None of my books states this
However, every serious book on the subject will tell you that CAM plants require less water. This is why they populate deserts and other such hostile environment. You can recognise a CAM plant because it has water in it's leaves and stem(like aloe vera)
Regards,
Andrew

"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

CAM plants require less water. Not C3 or C4.
C4 plants use a reaction way called C4 way. This reaction is followed by C3 way. C4 way provides more CO2 to the C3 way.
C3 plants do not have C4 way.
CAM plants also use C3 and C4 ways. the difference is that the stomas of CAM plants are opened during night and CO2 is stored.

Hope this helped.

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C4 plants are like crabgrass the ones that grow when it tends to be hotter. C3 is like bluegrass. The differene depedns on their intake of CO2. C4 bypass the need to use CO2 therefore they do not have to open their stromatas to let in CO2 for photosyntheseis.